The field of the invention is hydraulic valves. More particularly, the invention relates to hydraulic valves used to control an actuator, such as a hydraulic cylinder.
Hydraulic valves are widely used to control hydraulic actuators or cylinders, in various types of hydraulic systems. Hydraulic systems are widely used where relatively large forces are needed, such as lifting forces. Some of these hydraulic systems require precision control of the actuator, for example, hydraulic systems used in camera cranes, dollies, or pedestals.
Camera dollies are used in the television and motion picture industries to support and maneuver a camera. Typically, the camera dolly is on wheels and has an arm to raise and lower the camera. The camera dolly is generally moved by dolly operators or xe2x80x9cgripsxe2x80x9d, to properly position the camera, to follow the film or video sequence.
Various designs have been used to raise and lower a camera on a camera dolly. For example, U.S. Pat. No. 4,360,187 describes a two piece arm design for use in a camera dolly. The arm is raised and lowered via a hydraulic actuator and a control valve. Other camera dollies use a straight single piece beam arm or a telescoping pedestal lifted by a hydraulic or pneumatic actuator, such as described in U.S. Pat. No. 5,516,070.
The valves used to control a hydraulically driven camera dolly arm must meet certain design objectives. For example, the opening and closing characteristics of the valve should allow the camera dolly operator to accurately and easily control the speed and direction of the arm movement. The valve should also allow the arm to be accurately stopped at a selected elevation. In addition, the valve should operate silently, so as not to interfere with the sound track being recorded for the motion picture or video sequence.
U.S. Pat. Nos. 4,747,424 and 4,109,678, incorporated herein by reference, describe hydraulic valves which have been successfully used in camera cranes and dollies for many years. However, the valve described in U.S. Pat. No. 4,109,678 will occasionally generate fluid rushing or whistling sounds, especially on the xe2x80x9cdownxe2x80x9d side, as hydraulic fluid rapidly flows through the valve, when the camera dolly arm is quickly lowered. These sounds can be disruptive during filming. In addition, controlling this valve to begin movement of the camera dolly arm at a precise time can require a level of skill and experience, as the control handle must be turned by a certain amount before the camera dolly arm actually begins to move. The delay between control handle movement and arm movement results because the swash plate in the valve must turn sufficiently, before the valve cracks open. This characteristic can make precise control of the movement of the camera dolly arm more difficult. As split second timing is often needed to position a camera, the delay in arm movement can be a disadvantage. The delay may also induce less experienced grips to over-compensate by turning the control handle too far. This results in arm movement that is too fast, or that overshoots the desired camera lens height.
The valve described in U.S. Pat. No. 4,109,678 is a double pin or needle valve. A first needle opens or lifts off of a seat, to move the camera dolly arm up. A second needle openings to move the camera dolly arm down. Due to the design of this valve, the second needle may pop or jump slightly, as it openings, especially when the camera dolly arm is heavily loaded. This characteristic can cause a slight but noticeable disruption in smooth downward movement of the arm. As precision camera movement is often essential in filming, it would be advantageous to avoid this characteristic entirely. Similarly, such precision actuator movement would also be advantageous in hydraulic systems used in various other commercial, industrial, scientific or military equipment.
Accordingly, there remains a need for an improved hydraulic valve to control movement of a hydraulic actuator.
To these ends, an improved three-way hydraulic valve has first and second pins within a first and second bores of a valve housing, biased into sealing engagement with first and second valve seats, respectively. A swash plate or other actuator, linked to a valve control knob or lever displaces either the first pin, to open a first side of the valve or the second pin, to open a second side of the valve. The swash plate or actuator may also be moved into a stop position, where neither pin is displaced or separated from its valve seat, to close both sides of the valve. The first pin has a head which fits into or against the first valve seat. The head is located within a valve base having a channel connecting the first and second bores. A head extension extends from the head, away from the first valve seat, and into an opening or bore in the valve base. A seal in or at the bore, such as an o-ring, seals the head extension against the valve base, while allowing axial movement of the first pin.
With this improved design, hydraulic forces acting on the first pin are reduced or eliminated, thereby providing for very smooth and consistent valve operation even under heavy loading. The first pin is also better supported within the valve housing, providing quiet operation. The seal around the head extension acts as a dampener, reducing any fluid flow induced noise or vibration. The valve may advantageously be using to control a hydraulic cylinder or actuator.
The invention resides as well in subcombinations of the features, components, assemblies, and methods described and shown.